N,N′-diarylquinacridones have become useful materials and have necessitated synthetic methods for preparing them. In U.S. Pat. No. 6,376,107, Heuer et al disclose the preparation of N,N′-dialkylquinacridones by contacting unsubstituted quinacridones and alkyl halides with a base such as sodium hydride, in a solvent such as dimethylacetamide or dimethylformamide. This is however not extended to the case of aryl halides.
Radl et al, in a series of disclosures (Czech patents 262587, and 261338), disclose the reaction of 4-oxodihydroquinolines with nitroaryl halides with a base such as sodium hydride in a solvent such as dimethylformamide. The disclosure only teaches the use of aryl halides including nitro groups, and those skilled in the art will realize that aryl halides with other substituents, or no substituents at all, will not react as efficiently in this way.
It is a problem to be solved to provide a process for the synthesis of N,N′-diarylquinacridone compounds that is versatile and provides high yields and purity.